You do not need to tip tailors, local Thai restaurants,sales guys on the beach, massage ladys, policemen, lawyers,shopkeepers. Also high class hotels which do have a service charge levied on every item you consume do not expect tipping. But bell boys might give you special attention if you tip despite your knowledge.

Tip rates:

Waitress from 20 bath to 10% of charge.Bell Boys from 20 to 100 baht depending on their workload.